THE PHOTOPIC ERGs OF GUINEA PIGS AND HUMANS ARE ALMOST IDENTICAL.

Abstract

Abstract: : Purpose:To present the photopic ERG of the Guinea pig (GP) as the best rodent model of the human photopic ERG. Methods: Photopic luminance–response function (intensity: 0.62 to 2.84 log cd.sec.m^–2; background: 30 cd.m^–2), light adaptation effect (LAE) and flicker ERGs, obtained from albino GPs and normal human, were compared. Results: In contrasts to rats and mice, the cone ERG of GP includes a substantial a–wave resulting in a b–/a–wave ratio of 2.58±0.6, a value not significantly different (p>0.05) from human (2.47±0.6). Similarly, unlike rats and mice, the cone b–wave of GPs is followed by an i–wave, which is 15.6±0.8% of b–wave amplitude compared to 19.2±0.14% in human. FFT analysis also reveals high similarities, with three major frequency peaks at 30, 60 and 110 hertz in GPs and at 40, 70 and 150 hertz in human. Similarly, the intensity coding property of OP₂, previously demonstrated in human (3.65±0.4ms latency shift for a 1 log–unit intensity increase), is identical to that measured in GPs (3.8±0.6ms). Finally, as in human, use of a slow flicker (≤ 20Hz) also abolished the same OPs (OP₂, OP₃) while OP₄ was unaffected. However, while in human, the cone ERG doubles in amplitude with light adaptation, no similar enhancement could be demonstrated in the GP. Conclusions: Based on amplitude, frequency content, ERG and OP morphologies as well as previously published physiological features of the human ERG/OP, we believe that the cone ERG of the GP represent the best animal model of the human photopic ERG compared to rats or mice. The latter claim is also supported with our ability to generate in GPs, human–like pathological photopic ERG responses following intravitreal injections of pharmacological agents such as: APB, KYN or PDA. Finally, our inability to evidence a LAE in GPs, an effect also evidenced in mice and rats, should indicate new research avenues in order to identify the retinal mechanisms at the origin of this effect. Supported by CIHR and FRSQ Vision Network.

Keywords: electroretinography: non–clinical • electroretinography: clinical • drug toxicity/drug effects